A framework for integrating Mobile Hosts within the Internet

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Abstract

Host mobility and wireless access are two emerging design considerations
that pose challenging problems at all layers of the networking protocol
stack. This dissertation investigates their impact on the design of link,
network, and transport layer protocols. At the network layer, we have
designed and implemented a new routing architecture that allows the
current set of Internet standards to support routing to mobile hosts. At
the link and transport layers, we have designed mechanisms to improve
throughput over error-prone wireless channels.
At the network layer, the most crucial problem is that of routing. The
existing Internet routing mechanisms cannot route packets to hosts whose
points of attachment to the network change over time. Exploiting IP's
Loose Source Route option, we have designed and implemented a routing
scheme which provides location independent network access to TCP/IP
compliant mobile hosts. It also allows mobile hosts equipped with multiple
network interfaces to dynamically migrate active network sessions from one
network interface to another. The proposed scheme only requires the
addition of two new entity types, Mobile Routers and Mobile Access
Stations. These entities perform all required mobility-aware functions,
such as address translation, user tracking and location management. No
modifications to existing host or router software are required.
Although MobileIP provides continuous network connectivity to mobile
hosts, the effects of host movement and wireless medium characteristics
are often visible at the transport layer. We consider the effect of
wireless medium characteristics on the performance of Transmission Control
Protocol (TCP) sessions. Unlike wired networks, packets transmitted on
wireless channels are often subject to burst errors which cause back to
back packet losses. We show that TCP's error-recovery mechanisms perform
poorly when packets from a TCP session are subject to burst errors. Unlike
other approaches which require modification to TCP, our solution requires
enhancements only at the wireless link layer, thus making it applicable to
other transport protocols as well. We use a Channel State Dependent Packet
(CSDP) scheduler which takes wireless channel characteristics into
consideration in making packet dispatching decisions. Our results show
that the CSDP technique provides improved throughput, better channel
utilization, and fairness among multiple TCP streams.
(Also cross-referenced as UMIACS-TR-95-124)